1. Field of the Invention
The present invention relates to a write-once information recording medium, which includes bitmap information indicating whether each area has already been recorded or has not been recorded yet and on which a random write operation can be performed, and also relates to a method and apparatus for reading and/or writing from/to such a recording medium.
2. Description of the Related Art
Recently, various removable information recording media with huge storage capacities and disc drives for handling such media have become immensely popular. Examples of known removable information recording media with big storage capacities include optical discs such as DVDs and Blu-ray Discs (which will also be referred to herein as “BDs”). An optical disc drive performs a read/write operation by making tiny pits (or marks) on a given optical disc using a laser beam, and therefore, can be used effectively to handle such removable information recording media with huge storage capacities. Specifically, a red laser beam is used for DVDs, while a blue laser beam, having a shorter wavelength than the red laser beam, is used for BDs, thereby making the storage density and storage capacity of BDs higher and greater than those of DVDs. As for a BD-R, for example, a maximum storage capacity of as much as 27 gigabytes (GB) per recording layer has been realized.
For example, there is an optical disc that uses a phase change type recording material for its recording layer. A phase change type optical disc is irradiated with a laser beam and the atomic bonding state of a thin-film substance, which has been deposited on its recording layer, is locally varied with the energy injected, thereby writing information there. Also, when irradiated with a laser beam with much lower power than the one used for recording, the optical disc has its reflectance varied due to such a difference in physical condition. And if the magnitude of such a variation in reflectance is detected, the information stored there can be read out.
Phase change type optical discs include rewritable optical discs, on which information can be rewritten a number of times by using a phase change type recording material for its recording layer, and write-once optical discs, on which information can be written only once. If a mark edge write operation is performed on such a write-once optical disc, the disc is irradiated with a laser beam that has been modulated into a multi-pulse train to vary the physical condition of the recording material, thereby recording marks there. And information is read out from such a write-once optical disc by sensing a variation in reflectance between those recorded marks and spaces left between the marks.
However, as an optical disc is a removable information recording medium, probably there will be some defect on its recording layer due to the presence of dust or a scratch. Among other things, the higher the density of a recording medium, the more easily the recording medium will be affected by defects. That is why it has become a more and more common measure to take to carry out a defect management on not just rewritable optical discs (such as a BD-RE) but also write-once optical discs (such as a BD-R) as well to ensure the reliability of the data read or written (see Patent Document No. 1 (Japanese Patent Publication No. 4224391), for example).
FIG. 1 shows the arrangement of various areas on a write-once information recording medium (e.g., a dual-layer BD-R in this case).
Hereinafter, the arrangement of areas will be described with the dual-layer BD-R shown in FIG. 1 taken as an example.
On a BD-R, a read/write operation is performed on the basis of a block, which is an error correction unit and which is also called a “cluster”. One cluster consists of 32 sectors (each of which includes user data of 2048 bytes). Sectors are sometimes called “data frames”, too.
A write operation on a BD-R may be performed in either of the following two modes. One of the two is a sequential recording mode in which the write operation is performed continuously in a direction in which addresses increase from a certain point to which some data needs to be added. The other mode is a random recording mode in which the write operation is performed on arbitrary locations (i.e., unrecorded clusters). In the following example, however, the write operation is supposed to be performed in the random recording mode.
Each recording layer consists of an inner zone, a data area and an outer zone, which are arranged in this order from the inner edge of the BD-R toward its outer edge. In the following description, one of the two recording layers that has a lead-in area will be referred to herein as “L0 layer” and the other recording layer with a lead-out area as “L1 layer”. In a BD-R, the L0 and L1 layers are arranged in this order so that the L0 layer is located more distant from the laser beam incident surface than the other L1 layer.
On the innermost zone of the L0 layer, there is a control information area (which is called a “permanent information and control data (PIC) area). That control information area is defined as a read-only area while the disc is being manufactured. In the control information area, may be stored the type of that information recording medium (which may be BD-R or a BD-RE, for example), the number of recording layers included, disc's storage capacity-related information (including the first and last physical addresses of the data area of each recording layer, the channel bit length, and the nominal writing speed) and other kinds of disc information.
The data area of each recording layer consists of a user data area to write user data on and spare areas to provide a replacement for any defective part of the user data area.
Two spare areas are allocated to form inner and outer parts of the data area. One spare area that forms the inner part of the data area is called an “inner spare area (ISA)”, while the other spare area that forms the outer part of the data area is called an “outer spare area (OSA)”.
As shown in FIG. 1, TDMAs (including TDMA2, TDMA3, TDMA4 and TDMA5 in this case), which store disc management information and are sometimes called “additional temporary disc management areas (ATDMAs)”, may be allocated to the ISAs and OSAs. In the following description, however, such an ISA or OSA with an ATDMA will be regarded herein as forming together a single spare area.
The spare area may have any arbitrary size, which is set during formatting (initialization) processing, thereby determining the layout of the disc (i.e., the respective sizes of the user data area and the spare areas).
In addition, four disc management areas (DMAs) to store management information are arranged in total for the inner and outer zones.
FIG. 12 shows the arrangement of a DMA of the dual-layer BD-R.
As shown in FIG. 12(A), each of DMA1 through DMA4 consists of 64 blocks (=32 blocks×2 layers). Also, to ensure compatibility between BD-Rs and BD-REs, DMA1 through DMA4 are arranged at the same set of locations in both of these two types.
The first eight blocks of each DMA form an area to store disc management information, including the disc's layout information and information about recording statuses. On the other hand, the other 56 blocks thereof form an area to store defect management information including information about the locations of defects and their replacements.
In the dual-layer BD-R, four pieces of disc management information, each consisting of a disc definition structure (DDS) including disc's layout information (i.e., information about its format and status) and a space bitmap (SBM) indicating the recording status of the user data area, are arranged on a block-by-block basis in the first four blocks of each DMA.
All of these four DDSs store the same piece of information. As for the SBMs, on the other hand, L0 layer SBM and L1 layer SBM are stored alternately to manage the recording statuses of the user data areas on a recording layer basis.
To ensure compatibility with BD-REs, the remaining four blocks (i.e., the fifth through eighth blocks) are reserved and unrecorded (see Patent Document No. 2 (Japanese Patent Application Laid-Open Publication No. 2007-42277) and Patent Document No. 3 (PCT International Application Japanese National Phase Publication No. 2007-509453).
In a sequential recording mode, the recording statuses are managed by reference to sequential recording range information (SRRI) instead of the SBMs. Each user data area is divided into more than one sequential recording range (SRR). And by reference to the SRRI, the start address and the last recorded address of each SRR are managed as SRR entries, thereby managing the recording status of the user data area. In that case, the same piece of disc management information consisting of the DDS and the SRRI is written on each of those four blocks (i.e., the same number of blocks as that of the blocks with the SBMs) repeatedly on a block-by-block basis.
On the other hand, the same piece of defect management information (that forms a defect list) is written seven times on an eight block basis.
The same information is written on each of DMA1 through DMA4 (see FIG. 1). This is because if no management information could be retrieved from the DMAs, the read/write operation could not be carried out. That is why with the same piece of information written there multiple times, even if management information cannot be retrieved from any of those DMAs due to the presence of some defect such as dust or dirt, management information can still be retrieved from another one of the DMAs.
The same disc management information and the same defect management information are written a number of times for quite the same reason.
FIG. 13 shows the data structure of the DDS of the dual-layer BD-R.
The DDS is master information for use to manage a disc and is one sector of information including what needs to be used to define the arrangement of areas on the disc and to control the management information (i.e., slave information) such as the defect management information and SBMs.
Examples of those pieces of information that define the arrangement of areas on the disc include pieces of information about the sizes 1303, 1304 and 1305 of the spare areas, the logical last sector address 1302 of the user data area, and the ATDMA's sizes 1307, 1308 and 1309. On the other hand, examples of those pieces of information to control the management information include pieces of information about the recording mode 1306, DFL location information 1310 and 1311 indicating the locations where the DFLs are stored, and SBM location information 1312 and 1313 indicating the locations where the SBMs are stored.
As for the sizes of the spare areas, the sizes of three different kinds of areas, namely, the L0 layer inner spare area, outer spare areas, and L1 layer inner spare area, can be set. Specifically, the L0 layer inner spare area size 1303 indicates the size of ISA0 (see FIG. 1), the outer spare area size 1304 indicates the size of OSA0 and OSA1, and the L1 layer inner spare area size 1305 indicates the size of ISA1.
Just like the sizes of the spare areas, the sizes of three different kinds of ATDMAs, namely, the L0 layer inner ATDMA, outer ATDMAs, and L1 layer inner ATDMA, can be set. Specifically, the L0 layer inner ATDMA size 1307 indicates the size of TDAM2 (see FIG. 1), the outer ATDMA size 1308 indicates the size of TDMA3 and TDMA4, and the L1 layer inner ATDMA size 1309 indicates the size of TDMA5.
On the other hand, the size of the user data area can be determined by pieces of information about the storage capacity of the disc, including the first and last physical addresses of the respective recording layers' data areas that are stored in the PIC and the logical last sector address 1302 of the user data area that is stored in the DDS, and by the spare areas' sizes 1303, 1304 and 1305 that are also stored in the DDS.
In some cases, not all of those spare areas and ATDMAs can be defined only by formatting processing. Then, zeros will be stored in their sizes in the DDS.
Each DFL consists of eight blocks. And to manage the location information of each of those eight blocks, eight pieces of DFL location information are stored. Meanwhile, since the SBMs are managed on a recording layer basis, two pieces of SBM location information are stored for the L0 and L1 layers, respectively (see Patent Document No. 4 (Japanese Patent Application Laid-Open Publication No. 2008-293571), for example).
And the DDS header 1301 includes an identifier for use to determine whether this is a DDS or not.
FIG. 2 illustrates the data structure of each SBM.
The SBM 200 includes an SBM header 201 and bitmap information 202 indicating the recording status of the user data area. The SBM 200 is a piece of information to be stored in combination with a DDS of one sector and consists of 31 sectors.
The bitmap information 202 can be used to manage the recording status of the user data area by handling one block of the user data area as one bit and indicating a recorded block as one and an unrecorded block as zero, respectively (see Patent Document No. 2 (Japanese Patent Application Laid-Open Publication No. 2007-42277), for example).
The SBM header 201 includes layer information to indicate what recording layer this SBM is intended to manage. The SBM header 201 further includes the first physical address of the area to be managed by reference to the bitmap information 202 and the size of the bitmap information so as to indicate the size of the effective bitmap information and the range of the user data area to be managed by reference to that bitmap information. In addition, the SBM header further includes an identifier indicating whether this is an SBM or not.
And when finalize (also called “disc close”) processing is carried out to prohibit the user from newly adding any further piece of information to the disc and make the disc a read-only one, management information indicating the latest state of the disc is written on the DMA.
FIG. 14 shows the arrangement of areas in a temporary disc management area (TDMA) on the dual-layer BD-R.
In the TDMA, the respective data structures of its SBMs, DDSs and DFL themselves are identical with those of the DMA. In the TDMA, however, the DFL is stored in a different number of blocks, each DDS is stored at the last sector of its associated block, and a DDS is also added to the DFL being written, which are some of the differences between the TDAM and the DMA.
A TDMA is an area that is provided to get defect management done on a BD-R, of which the DMAs cannot be overwritten. That is why by adding management information to the TDMA and updating it while the disc is being finalized, defects and the recording status of the disc can be managed.
For that reason, to use the area as effectively as possible and avoid using the area up, nothing but required information is written on the TDMA. Therefore, if there are only a few defects and the DFL needs to cover just four blocks, the information will be written on only those four blocks.
The DDS is written on the last sector of each block so that the latest DDS never fails to be stored on the sector that is located just before the boundary between the recorded and unrecorded areas of the TDMA. In that case, just by searching for the boundary between the recorded and unrecorded areas of the TDMA and scanning the sector that is located just before the boundary that has been found, the latest DDS can be obtained. Likewise, when the DFL is updated, the DDS is written for quite the same reason (see Patent Document No. 1 (Japanese Patent No. 4224391), for example).
In this manner, defect management can get done on a BD-R.
Recently, the storage capacities of optical discs have been further increased year by year. To increase the overall storage capacity of an optical disc, the storage density per recording layer can be increased by shortening marks and spaces to record and the track pitch. Or the overall storage capacity can also be increased by increasing the number of recording layers to be stacked in a disc.
However, if the storage capacity per recording layer is increased by raising the storage density, the size of the user data area should be increased, too. In the sequential recording mode, the SRRI, which is used to manage the recording status of the user data area and which will be stored along with the DDS, is supposed to be managed with the start address and the last recorded address of the SRR. And therefore, the SRRI does not depend on the size of the user data area and the size of the DDS and the SRRI combined is one block.